1. Field of Invention
The present invention relates to vibrating tools. More particularly the present invention is directed to vibrating, hand-operated, surface-finishing tools.
2. Description of the Prior Art
The present invention is a unique vibrating tool which may advantageously be used to modify the texture or character (i.e. the "finish") of a surface of a work material. The following disclosure principally describes the preferred embodiment of the invention and its use in advantageously finishing an exposed surface of a plastic concrete mass. It will be understood, however, that similar tools constructed in accordance with the present invention may be used to modify the texture or character of an exposed surface of many other materials, particularly plastic or wet materials such as plaster, wet soil, cement and the like.
After concrete is initially laid, it must be worked while it is wet in order to provide a smooth, homogeneous mixture. Working the concrete helps settle the concrete and helps to densify and compact the concrete during finishing. The working also removes air voids and brings excess water and fine aggregates to the surface for subsequent finishing.
After the initial finishing stages are complete a more detailed work frequently commences, generally by means of a hand-held float in attempting to further compact the concrete for purposes including the driving of suspended gravel downwards, and developing a wetted surface slurry or soup-like finish, while further driving out air pockets and the like for preparing the surface for final finishing. Thereafter, when the surface slurry is thus formed, it is conventional to employ a smoothing or finishing trowel to develop a very smooth surface, and to employ specialty tools (such as edgers) to provide finishing touches to the work (such as curved edges or the like).
It is generally known that, if not worked, the surface of wet concrete would take on a highly undesirable rough and uneven finish which, after partial setting of the concrete, would render the surface difficult if not impossible to finish to the desired smooth and even consistency.
For this reason, it has long been known in the art that in the act of providing a first general compacting, tamping, screeding or other such operation following the laying or dumping of the mix, various large vibrating devices may be beneficially employed. Illustrative embodiments of such large vibrating tampers or the like may be seen in U.S. Pat. Nos. 3,306,174 to Wardell, 2,289,248 to Davis, 1,955,101 to Sloan, and 2,209,965 to Mall. These devices generally include a rather large flat base plate, a heavy and bulky vibratory mechanism disposed thereon, and an elongate handle attached thereto for moving the large plate across the concrete surface. Such devices are generally intended to provide a general smoothing and compacting operation over a large area.
When the worker has progressed to the aforementioned finishing stage wherein it is desired to provide a highly smoothed surface finish, a variety of prior vibrating hand trowels may be employed with varying degrees of success. Representative examples of such trowels which are primarily for smoothing or finishing work, may be seen in U.S. Pat. Nos. 3,376,798 to Bodine, 2,514,626 to Clipson, and 2,411,317 to Day et al. Whereas such trowels are, in contrast to the aforementioned larger devices, intended for hand-held operation, they retain several characteristics of the larger apparatus such as being of a rather awkward large and heavy construction, illustrative of which is the trowel disclosed in the Day patent. Whereas such features may in fact be beneficial with respect to the larger devices, in a hand-held tool this bulk, weight, and complexity may render the tool totally impractical for use, particularly in view of the fact that the operator is typically working for long periods of time on his knees and often in awkward positions. It must be recognized that these trowels are conventionally used primarily in the finishing operations wherein a great deal of vibratory energy is not required inasmuch as a mere final smoothing of the surface slurry is being effected. In these instances, a much less bulky vibrating means might be provided although, as discussed above, most designs nevertheless continue to suffer from undue weight, bulk and the like. Notwithstanding, a variety of such vibrating means have been attempted to be employed including plunger-type vibrators (as disclosed in the patent to Clipson), air driven turbine vibrators (as disclosed in the patent to Day), and even sonic air-driven orbiting-mass type vibrators (as illustrated in the patent to Bodine).
Another prior vibrating hand trowel is disclosed in U.S. Pat. No. 5,234,283 to Adkins. In this trowel the vibratory mechanism is mounted inside the handle. The vibratory mechanism vibrates a rigid metal blade of relatively large mass by "pushing off" of the handle in an oscillating fashion. An inherent consequence of this construction is that the handle vibrates as much or more than the blade of the trowel which contacts the wet concrete. These vibrations cause discomfort and difficulty of use for the operator. As a means of reducing the amount of uncomfortable vibrations transmitted through the handle to the operator, this device, in practice, is typically manufactured such that the handle/vibrator mechanism is of relatively high mass. As discussed above with respect to other prior vibrating finishing tools, it is undesirable for such trowels to be heavy and bulky. Also, because only one vibrating mechanism (i.e. located in the handle and attached to the blade of the trowel at one point) is used to drive the entire blade, the blade must be constructed of particularly rigid, (and therefore frequently heavy and thick) material in order to cause the entire blade to vibrate in phase. A more desirable hand tool would incorporate characteristics that would cause the majority of the vibratory energy to be transmitted to the work concrete through the bottom of the device in an efficient and uniform manner and not to the operator through the handle.
Prior patents in this art are relatively silent regarding determination of the frequency at which the vibrations should be applied to the work concrete. Because little attention is given in the prior art to the importance of determination of the frequency at which vibrations should be applied to the work material, prior vibrating concrete finishing tools typically are not provided with means by which tools' vibration frequencies can be readily changed by the user. Consequently, many prior devices do not vibrate the concrete very efficiently. Most prior concrete finishing vibrating hand tools are operated simply by turning a switch having only two settings: on or off. However, in practice each batch of concrete delivered to a job site is different from the next, and a different frequency of vibration may be required from one batch to another in order to cause the desired slurry to be formed more quickly and more efficiently. This is because the natural frequency of each batch may be different due to the amount of water, concrete and aggregate mix that make up each particular batch. Accordingly, it is desirable to provide a vibrating hand tool with multiple frequency settings.
Another problem with the prior art relates to the bulk of the device itself, as well as the bulk of the power supply. Some prior vibrating hand trowels (such as the one disclosed in the patent to Adkins) consist of an electric cord running from the tool to a bulky battery pack which is mounted in a belt and placed around the operator's waist. Because of the low electrical-to-mechanical power transmission efficiency, and because of the low vibrational energy inefficiency from the actuator to the work medium of prior devices, it is typically necessary to provide such prior devices with large power supplies. Thus, prior vibrating concrete finishing tools are typically provided with battery packs which are large and heavy, and, if worn on a waist belt, uncomfortable to the operator. In addition, in such prior devices the length of the cord is such that it may be inadvertently dragged through the concrete. A hand trowel with either a battery pack in the handle or a less bulky hip-pack with a shorter cord would therefore be more desirable.
Prior methods of smoothing plastic concrete using a hand trowel are not effective in removing water or air pockets that may be trapped in the concrete. A simple hand trowel typically consists of a handle and a flat metal blade. The trowel is used to smooth the top layer of poured concrete, but has little effect on water or air below the surface of the concrete. Conventional hand trowels are also hard to use near walls or corners because they must be wiped back and forth over the surface of the plastic concrete and the wall often is an obstruction. Conventional hand trowels are also difficult to use for long periods of time because of the high amount of friction between the blade of the tool and the concrete.
Gasoline powered vibrating finishing tools cause noise pollution, harmful exhaust emissions, and do not produce a high enough output frequency to effectively vibrate the medium. They also are hard to control and virtually impossible to use in closed quarters or at edges and corners, because they are large and bulky and do not operate well adjacent protruding vertical structures (i.e. walls).
Other types of prior vibratory hand tools are difficult to handle because, when the vibration is applied, the entire tool vibrates causing difficulty for the operator.